Year	Years
1970	1.66
1971	1.71
1972	1.77
1973	1.82
1974	1.88
1975	1.95
1976	2.01
1977	2.07
1978	2.14
1979	2.21
1980	2.28
1981	2.36
1982	2.43
1983	2.51
1984	2.59
1985	2.68
1986	2.76
1987	2.85
1988	2.95
1989	3.04
1990	3.14
1991	3.24
1992	3.35
1993	3.45
1994	3.56
1995	3.68
1996	3.79
1997	3.9
1998	4.02
1999	4.13
2000	4.25
2001	4.37
2002	4.49
2003	4.61
2004	4.74
2005	4.86
2006	4.99
2007	5.12
2008	5.25
2009	5.39
2010	5.53
2011	5.66
2012	5.8
2013	5.95
2014	6.09
2015	6.23